A negation in math is where you take a statement and make it say the complete opposite of the original.
Examples:
1) The ball is red. Negation: The ball is NOT red.
2) The ball was either blue or green. Negation: The bath is not blue and not green.

Negation means the opposite. In symbolic logic, the negation of a statement is one that means exactly the opposite. For a statement p, the negation is the statement ~p. An example:
p: I am a bride.
~p: I am not a bride.

In mathematics, negation is the logical operation that takes a statement and changes is it to a statement whose true or false value is opposite that of the original statement. So, if the statement is two plus three equals five, the negation is two plus three is not equal to five.